Scotty
I am selling my 2018 automatic RAV4 LE AWD with just 17850 miles, as I am moving out of the country. I had the oil changed & tires rotated at 15,500 miles. Would cleaning the engine be beneficial when I put it up for sale? If so, should it be done professionally or can I do it?
Toyotachick
only if it's really bad. Nobody expects a spotless engine.
I always have mine detailed before I sell my cars. Makes it stand out from the next guy.
when I see a shiny engine, all I can think is, "hmm, what kind of leaks is he trying to hide" 
Lol well it could be taken that way too. For me, it depends on how dirty we are talking. If it is normal dirty...meh..not a deal breaker. But I've seen some that look like they just came through the Sahara with no hood on. In that case....nah. lol.
You have a very low mileage car and it is expected to be relatively clean but do not go crazy with cleaning.
I think so, to make it more presentable - no need to overdo it, however. See below for tips:
https://carkiller.com/scottykilmer/qa/cleaning-your-engine-bay/#post-106303
Avoid using water, use WD40 instead
